The present invention is relative to a device for dehydrating sludge, especially dilute sludges, in accordance with the generic part of claim 1.
Various sludges such as recycled sludge, digesting sludge or fresh sludge, etc. accumulate in the preparation of waste water, especially in sewage treatment plants. These sludges have at times a very high water content that should be reduced. The reducing of the water content simplifies in particular the managing of the sludge as well as, for example, significantly reduces the disposal costs. In particular, mechanical systems are also used for the concentrating of sludges. Usually a conditioning of the sludge with polyelectrolytes (auxiliary flocculation agents) are employed for a mechanical concentrating of sludges. These polyelectrolytes bring about a flocculation of the sludges treated in this manner so that the separation and filtration of the free supernatant water is better possible. As a rule, a volumetric decrease of approximately 80%-90% is possible with mechanical systems in combination with the conditioning of the sludge. In particular, this also makes it possible to render subsequent method steps in the purification of waste water more economical and more effective.
DE 39 42 561 C1 teaches a device that operates continuously and automatically to dehydrate a sludge laced with an auxiliary flocculation agent (e.g., polyelectrolyte). In this system, that operates with a transport worm, conditioned sludge is conducted into a cylindrical wedge-wire screen and transported there by the transport worm continuously from the inlet of the screen cylinder to the discharge of the screen cylinder. The device is set up at an angle of approximately 30xc2x0 between the inlet and the discharge, as a result of which the flocculated sludge is continuously raised with the transport worm. In addition to the transport, a rotation of the flocculated sludge also takes place, which amplifies the exit of the filtrate water through the wedge-wire screen. The entrained solids remain in the cylinder and are separated at its end via a chute. The filtration time is regulated via the transport speed of the worm.
Usually, a conditioning of the sludge is also carried out in centrifugal systems for separating water from sludges. The work is performed at high rotation speeds in these systems, as a result of which solids settle on the sieve jacket of the centrifuge. The separated water collects in the center of the sieve jacket and flows via an outlet tube out of the jacket. The solid is transported by the centrifuge rotor via a control dam out of the jacket. In addition, devices with rotating sieve drums are also known. The flocculated sludge is centrally introduced into a sieve drum, during which a rotation of the flocculated sludge takes place by means of the rotation of the sieve drum in combination with so-called transport baffles. The supernatant water passes through the sieve surface of the drum to the outside, during which the solid is concentrated in the drum. The solid is ejected by the rotation of the drum through the mounted baffles, that generate a thrust, at the other end of the drum. These sieve drums are mounted at various inclinations between 0xc2x0 and 10xc2x0 of their axis.
Furthermore, band filter systems are known that are also designated as band thickeners or straining bands. They also work with sludge conditioned with polyelectrolytes. The flocculated sludge is placed and distributed on a polyester band cloth. The supernatant water flows through the sieve band by gravitation, during which the solid is deposited on its surface. A concentration of the sludge takes place by the advance of the filter cloth over rollers and, e.g., by means of other mounted components such as, e.g., baffles. The sludge moves along the thickening stretch by virtue of the advance of the band-shaped filter cloth and is dumped into a funnel after it has been concentrated.
The known devices have the disadvantage that they are expensive to construct and have a large space requirement.
DE-A 27 47 506 teaches a method of drying pasty, aqueous sludges in which the sludge is spread out on a horizontally aligned sieve surface and brought in contact with warm waste gases. The sludge is treated during the rotation of the sieve surface with various tools that engage into the sludge surface.
BE-A 564 675 teaches a device for dehydrating sludge in which the sludge is placed on rectangular sieve surfaces arranged in a box that are put in motion by vibrations. The box can be put in an inclined position by supports of varying heights.
The present invention has the problem of designing a device for dehydrating sludge, especially, dilute sludges, in such a manner that a device is created that saves space and is simply designed and assures a good separation between liquids and solids, in particular in the case of conditioned sludges. The invention solves this problem with the features of the device in accordance with claim 1.
The design of the device for dehydrating sludge in accordance with the invention brings it about in an advantageous manner that it can be compactly and economically constructed. The circular design of the sieve surface makes possible an advantageous utilization of the surface and therewith a low space requirement and at the same time a low expenditure for material. The rotatable design makes it possible to transport the sludge to be dehydrated in the device with only one moved part and at the same time to remove the dehydrated sludge out of the device. In addition, this embodiment simultaneously permits other components that cooperate with the device to be designed in an especially short and space-saving manner.
The design of the sieve surface with its axis inclined relative to a horizontal line brings it about that even water or liquids in general that settled on the surface of the sludge can be separated from the sludge. They flow off as a function of the slope. In an advantageous further development of the invention the device comprises a drive device, as a result of which the rotating of the sieve surface and therewith a transport of the dehydrated sludge is possible in an especially simple manner. It is advantageous if the sieve surface is supported by a shaft arranged vertically to the sieve surface. It is especially favorable if this shaft is arranged in the center of the circular sieve surface. Moreover, this shaft has the advantage that the sieve surface can also be caused to rotate, that is, is driven by the shaft. In another advantageous embodiment of the invention the sieve surface is supported in a rotatable fashion by its edge, e.g., on guides of the housing and can advantageously also be driven by its edge, that is, put in rotation.
The device advantageously comprises a supply line for sludge and also an outlet for separated water. It is likewise especially advantageous to provide a discharge for the dehydrated sludge. This makes it possible for the device to be able to operate continuously. In addition, this also makes it possible that the device can be used in an automatic system. The supply line for the sludge is advantageously arranged above the sieve surface thereby and the outlet for the separated water is arranged below the sieve surface, as a consequence of which natural gravity is utilized for dehydrating the sludge. The arrangement of supply and outlet distributed over the circumference brings it about that a reliable separation between water and solids can take place. To this end the container, in which the sieve surface is advantageously arranged, comprises a perforation. In an advantageous further development of the invention the container comprises a cover, as a result of which the sludge can be treated separated from its environment. This is especially advantageous when the device is used in closed spaces since sludges can also entrain components that are dangerous to health.
In an especially advantageous further development of the invention the drive device is mounted above the cover, which makes a simple and economical design of the device possible. The pivotable design of the container relative to a horizontal line can achieve an inclination of the sieve surface with the advantages associated therewith and at the same time the container can be emptied of water over only one side in which the separated water then collects. In an advantageous further development of the invention the container comprises supports for this purpose that carry the entire device. A changing of these supports makes it possible to adjust the inclination of the axis. In an advantageous embodiment the adjustability is designed in such a manner that inclinations of the sieve surface axis between 0xc2x0 and 30xc2x0 are made possible. In an advantageous further development of the invention the sieve surface consists of a carrier surface covered for its part with the actual sieve. This makes it possible to design the sieve surface economically since the function of mechanical stability and that of a sieve, namely, separating out particles of dirt, are separated from one another. In an especially advantageous further development of the invention the sieve consists of a microsieve covering [fabric] drawn over the carrier surface of the sieve surface. In another advantageous embodiment of the invention the sieve consists of a polyester cloth covering. A sintered, pre-tensioned microsieve without carrier surface can also be used.
In an economical embodiment the carrier surface consists of a perforated sheet, which simultaneously assures sufficient mechanical stability, an economical design and operational reliability. This sheet is formed in an especially advantageous manner from a corrosion-resisting material, e.g., stainless steel (high-grade steel). In an especially advantageous further development of the invention the sieve surface is associated with a wiper that can be, e.g., simply arranged stationarily. The dehydrated sludge is then separated in a simple manner from the sieve surface by the rotation of the sieve surface. The wiper can be advantageously provided with brushes or comprise a wiper lip designed, e.g., in an advantageous manner from rubber or some other suitable material, e.g., plastic.
In an especially advantageous further development of the invention the sieve surface comprises a cleaning device which brings it about in an advantageous manner that the sieve surface can not be clogged by the solid components of the sludge and that these solid components can be removed, thus increasing the operational reliability of the device. In an especially advantageous further development of the invention the cleaning device is designed as a spray-jet system, as a result of which a reliable operation is assured and as an advantage no additional measures or means have to be used. For the sake of simplicity the separated water can be used with advantage for the operation of the spray jets. The especially advantageous arrangement of the cleaning device, viewed in the direction of movement of the sieve surface after the wiper and thus in front of the sludge feed, brings it about that the sieve surface is cleaned before new sludge is applied onto it in order that the passage of the water and therewith a dehydration of the sludge is reliably assured. To this end the cleaning device is advantageously arranged below the sieve surface since this assures an especially good cleaning of the openings of the sieve surface.
In a further advantageous further development of the invention the sieve surface is provided with a pressing device advantageously designed as a roller. This device rests on the sludge in order to place it under pressure in this manner so that more water can be separated off. Due to the advantageous design as a roller it can be moved along with the moving sludge so that no delay or backup of the sludge takes place. The load that the roller exerts on the sludge can be designed in an advantageous manner to be adjustable in that, e.g., the roller is advantageously designed to be hollow in order that it can be filled, e.g., with water to increase its intrinsic weight. In a further advantageous embodiment of the invention grippers are provided that are stationarily arranged in such a manner that they engage into the sludge as a result of the rotation of the sieve surface and thoroughly mix it or loosen it up, as a result of which, e.g., trapped water that has already been separated is freed and can be separated. This rearrangement of the sludge therefore increases the amount of water separated off.